{"id":68371,"date":"2025-08-19T12:32:14","date_gmt":"2025-08-19T09:02:14","guid":{"rendered":"https:\/\/afaghhosting.net\/blog\/cve-2025-38553-linux-kernel-netem-qdisc-tree-duplication-vulnerability\/"},"modified":"2025-08-19T12:32:14","modified_gmt":"2025-08-19T09:02:14","slug":"cve-2025-38553-linux-kernel-netem-qdisc-tree-duplication-vulnerability","status":"publish","type":"post","link":"https:\/\/afaghhosting.net\/blog\/cve-2025-38553-linux-kernel-netem-qdisc-tree-duplication-vulnerability\/","title":{"rendered":"CVE-2025-38553 &#8211; Linux Kernel Netem Qdisc Tree Duplication Vulnerability"},"content":{"rendered":"<p><strong>CVE ID : <\/strong>CVE-2025-38553<br \/>\n<br \/>\n<strong>Published : <\/strong> Aug. 19, 2025, 6:15 a.m. | 1\u00a0hour, 58\u00a0minutes ago<br \/>\n<br \/>\n<strong>Description : <\/strong>In the Linux kernel, the following vulnerability has been resolved:<\/p>\n<p>net\/sched: Restrict conditions for adding duplicating netems to qdisc tree<\/p>\n<p>netem_enqueue&#8217;s duplication prevention logic breaks when a netem<br \/>\nresides in a qdisc tree with other netems &#8211; this can lead to a<br \/>\nsoft lockup and OOM loop in netem_dequeue, as seen in [1].<br \/>\nEnsure that a duplicating netem cannot exist in a tree with other<br \/>\nnetems.<\/p>\n<p>Previous approaches suggested in discussions in chronological order:<\/p>\n<p>1) Track duplication status or ttl in the sk_buff struct. Considered<br \/>\ntoo specific a use case to extend such a struct, though this would<br \/>\nbe a resilient fix and address other previous and potential future<br \/>\nDOS bugs like the one described in loopy fun [2].<\/p>\n<p>2) Restrict netem_enqueue recursion depth like in act_mirred with a<br \/>\nper cpu variable. However, netem_dequeue can call enqueue on its<br \/>\nchild, and the depth restriction could be bypassed if the child is a<br \/>\nnetem.<\/p>\n<p>3) Use the same approach as in 2, but add metadata in netem_skb_cb<br \/>\nto handle the netem_dequeue case and track a packet&#8217;s involvement<br \/>\nin duplication. This is an overly complex approach, and Jamal<br \/>\nnotes that the skb cb can be overwritten to circumvent this<br \/>\nsafeguard.<\/p>\n<p>4) Prevent the addition of a netem to a qdisc tree if its ancestral<br \/>\npath contains a netem. However, filters and actions can cause a<br \/>\npacket to change paths when re-enqueued to the root from netem<br \/>\nduplication, leading us to the current solution: prevent a<br \/>\nduplicating netem from inhabiting the same tree as other netems.<\/p>\n[1] https:\/\/lore.kernel.org\/netdev\/8DuRWwfqjoRDLDmBMlIfbrsZg9Gx50DHJc1ilxsEBNe2D6NMoigR_eIRIG0LOjMc3r10nUUZtArXx4oZBIdUfZQrwjcQhdinnMis_0G7VEk=@willsroot.io\/<br \/>\n[2] https:\/\/lwn.net\/Articles\/719297\/<br \/>\n<br \/>\n<strong>Severity:<\/strong> 0.0 | NA<br \/>\n<br \/>\nVisit the link for more details, such as CVSS details, affected products, timeline, and more&#8230;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>CVE ID : CVE-2025-38553 Published : Aug. 19, 2025, 6:15 a.m. | 1\u00a0hour, 58\u00a0minutes ago Description : In the Linux kernel, the following vulnerability has been resolved: net\/sched: Restrict conditions for adding duplicating netems to qdisc tree netem_enqueue&#8217;s duplication prevention logic breaks when a netem resides in a qdisc tree with other netems &#8211; this &hellip;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[],"class_list":["post-68371","post","type-post","status-publish","format-standard","hentry","category-vulnerability"],"_links":{"self":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/68371","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/comments?post=68371"}],"version-history":[{"count":0,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/68371\/revisions"}],"wp:attachment":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/media?parent=68371"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/categories?post=68371"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/tags?post=68371"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}